Electric lamp stem



Nov. 1, 1966 G. N. ELLIOTT ELECTRIC LAMP STEM Filed Nov. 1, 1961 INVENTOR.

T T w .L L E N E G R O E G ATTORNEY United States Patent Ofiice Patented Nov. 1, 1966 3,283,197 ELECTRIC LAMP STEM George N. Elliott, Somerville, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Nov. 1, 1961, Ser. No. 149,391 4 Claims. '(Cl. 313-266) This invention relates to electric lamps and particularly to stems used in such lamps.

Such lamps generally include a sealed light-transmitting envelope having at least one end closed by a stem.

The stem is usually made of glass or the like and includes a skirt-like portion, or flare, and a pressed portion, or press. The lead-in wires are sealed through the press, and the flare is sealed around its perimeter to an opening in a glass tube or bulb.

The stem also contains an exhaust tube which extends from below the flare to an opening or blow-hole in the press. The envelope is exhausted through this tube, which is thereafter sealed.

The blow-hole is sometimes placed on the top of the press, in which case the spacing of the lead-in wires must be great enough to allow the positioning of the blowhole between them. This is not always possible, and even when it is, the lead-in wires may be burned by the heat used to form the blow-hole. The manufacture of a stem with a top blow-hole is more diflicult, and the exhaust tube leading to it is often easily broken off.

For such reasons, the side blow-hole is generally preferred for fluorescent lamps. Such a blow-hole is formed in the side of the stem near the bottom of the press. The lamp envelope generally has a phosphor coating, even near the stern, and the flushing gas usually introduced into the envelope through the exhaust tube and blowhole will be directed toward the phosphor coating. Since the flushing gas may be at a pressure of tens of millimeters of mercury, it can strike the phosphor coating with considerable force, blowing it away and forming a clear spot on the bulb, often referred to as blown coating. Since there is no binder in the phosphor coating to make it adhere to the bulb wall, such blown coating occurs quite readily when stems with side blow-holes are used, particularly in fluorescent lamps of circular types, where the contour of the lamp tube puts the blow-hole close to the tube wall.

My invention overcomes the above disadvantages by running a groove from the top of the press, between the lead-in wires, to the top of a side blow-hole. I find that the groove so formed permits the gases to emerge from the blow-hole in a direction nearly parallel to the longitudinal axis of the bulb, thereby avoiding impingement on the phosphor coating on the inside wall of the envelope.

In a preferred embodiment of my invention I form two blow holes, one on either side of the press, and shape a channel also on each side of the press, forming two exit paths for the emerging gases which not only reduces the velocity of the gases but increases the pumping efficiency of the stern since I have doubled the exit area.

Thus by my invention I am able to tolerate an increase in gas pressure during lamp processing, if desired, eliminate blown coating defects and the cost thereof, all without sacrificing stem strength and economical and etficient manufacture.

The groove in the press can be formed by pressing suitably shaped jaws against the press while the latter is softened by heat.

Other objects, advantages and features of the invention will be apparent from the following specification taken in accordance with the accompanying drawing, in which:

FIG. 1 is a side view of a fluorescent lamp stern according to the invention;

FIG. 2 is a cross-sectioned, broken-01f view of the same stem in a fluorescent lamp;

FIG. 3 is a top view of the stern; and

FIG. 4 is a view of a jaw for forming the groove in the press.

In FIGURE 1, the stem 1 has a flared-out portion 2, usually referred to simply as a flare, which merges into a generally cylindrical portion 3, the top of which is flattened to form a press 4. Lead-in wires 5, 6 are sealed through the press 4, extending above the press to support and make electrical contact with a filament 7, which is generally a coiled-coil or triple coil of tungsten wire, and coated with electron emitting oxides in the usual manner. The filament 7 is connected to the lead-in wires 5, 6 by bending said wires back upon themselves near their ends, to clamp the filament between the main portions of the lead-in wires 5, 6 and the bent-over portions 8, 9. An exhaust tube 10 extends axially into the flare, being sealed to the blow-holes 11, 12, as shown in more detail in FIG- URE 2. Two such holes 11, 12 are shown in the figures but one will usually be suflicient, in which case the opening 12 will not be present.

In FIGURE 2 the flare 2 is shown sealed at its outside rim to the end 13 of a fluorescent lamp tube 14. A phosphor coating 15 is applied to the inner surface of glass tube 14, including end 13. The flare 2 is shown sealed to a substantially straight tube 14; if the tube 14 were curved as in a circular lamp, it would be nearer to the blow-hole 11, as shown in phantom tube 21.

Above the openings 11, 12 the grooves 16, 17 extend upwardly nearly to the top 18 of the press 4. The top portion of press 4 has lips 19, 20 which extend outwardly over the grooves 16, 17.

A top view of the stem of FIGURE 1 is shown as FIGURE 3, with the filament 7 removed in order to permit the details of the top of the stem to be clearly shown.

The grooves 16, 17 can be formed in any suitable manner, for example by pressing the raised portion 22 of a jaw 23 against the portion of the press 4 where the groove is desired, while the press is hot enough to make the glass soft, for example, shortly after the lead-in wires 5, 6 are sealed through the press 4 and the press flattened out.

In operation, when gas is admitted to the lamp tube 14 exhaust tube 10 and the blow-holes 11, 12 it will tend to enter the tube in a nearly axial direction, and will not be deflected directly into the fluorescent coating 15, as it would if the grooves 16, 17 were not present. The lips 19, 20 at the top of the stem serve to prevent the entering gas stream from directly impinging upon the filament 7. Such direct impingement might remove some of the electron-emitting coating from filament 7, or might have some other adverse effect upon it. When such direct impingement is not harmful, because of high adhesion of the electron-emitting coating to the filament 7, the lips 19, 20 can be omitted, and the groove extended all the way to the top 18 of press 4.

In one specific example of the invention the flare 2 at its larger end was about 1 /2" in diameter, with the roughly cylindrical portion 3 being about 1" in diameter. The blow-holes 11, 12 had a diameter of about 0.08 and the grooves 17, 16 were about X9 wide and about deep. The grooves 16, 17 were made to have an arcuate cross-section, the radius of the arc being about The grooves 16, 17 extended upwardly a distance of about 4 millimeters and the lips 19 and 20 were about 1 millimeter thick.

The stem was sealed into one end of a so-called 40 watt T12 glass tube, that is, a tube about 1 /2" outside diameter, the tube being about 4 feet long and having another stem of the same type closing its other end. Such an arrangement is generally used in the 40 watt straighttube fluorescent lamp. In a circular fluorescent lamp, the tube is bent to an arcuate or circular shape in the usual manner, as indicated by the phantom tube 12.

Although the lead-in wires 5, 6 are each shown as a single wire, in practice they will generally be of a metal which seals to glass, such as the copper-content nickelrim alloy, generally known as dumet in the portion of the wire passing through press 4, and of nickel or another suitable support-wire metal in the portion above, or extending slightly into the top of press 4. The portion below press 4 may be a metal, such as copper, suitable for connection to a contact base.

What I claim is:

1. An electric lamp including an envelope having an opening and a stem closing said opening, said stem comprising a substantially fiat press through which at least two lead-in wires extend, a filament inside said envelope and connected to said lead-in wires, an exhaust tube sealed to form a blow-hole at the side of the bottom of said press, a substantially flat groove in said press and extending from said blow-hole to the top of said press, and a lip extending outwardly over said grooves from the top of said press.

2. An electric lamp including an envelope having an opening and a stem closing said opening, said envelope having a coating of phosphor on its interior surface near said stem, said stern comprising a substantially fiat press through which at least two lead-in wires extend, a filament inside said envelope and connected to said lead-in wires, a coating of electron-emitting material on said filament, an exhaust tube sealed to form a blow-hole at the side of the bottom of said press, and a rectangular groove in said press and extending from the top of said blowhole to the top of said press, the width of said groove be- 4 ing smaller than the diameter of said blowhole, said groove intersecting the top of said blowhole.

3. An electric lamp including a glass tube open at at least one end, a stem closing the open end, and a coating of phosphor on the inside surface of said tube at said end, said stem comprising a substantially flat press through which at least two lead-in wires extend, a filament inside said envelope and connected to said lead-in wires, a coating of electron-emitting material on said filament, an exhaust tube sealed to form a blow-hole at the side of the bottom of said press, a groove in said press and extending from said blow-hole to the top of said press, and a lip extending outwardly over said groove from the top of said press.

4. An electric lamp including an envelope having an opening, a coating of phosphor on the inside surface of said envelope near said opening, and a stem closing said opening, said stem comprising a substantially flat press through which at least two lead-in wires extend, a filament inside said envelope and connected to said lead-in wires, a coating of electron-emitting material on said filament, an exhaust tube sealed to form a blow-hole on each side of said press, and a groove from each blow-hole to the top of said press, and a lip extending outwardly over said groove from the top of said press.

References Cited by the Examiner UNITED STATES PATENTS 1,906,819 5/1933 Severim 313-316 2,057,305 10/1936 Lyle 313-266 2,279,907 4/ 1942 Atchley 313109 HERMAN KARL SAALBACH, Primary Examiner. ARTHUR GAUSS, DAVID J. GALVIN, Examiners. S. CHATMON, JR., Assistant Examiner. 

1. AN ELECTRIC LAMP INCLUDING AN ENVELOPE HAVING AN OPENING AND A STEM CLOSING SAID OPENING, SAID STEM COMPRISING A SUBSTANTIALLY FLAT PRESS THROUGH WHICH AT LEAST TWO LEAD-IN WIRES EXTEND, A FILAMENT INSIDE SAID ENVELOPE AND CONNECTED TO SAID LEAD-IN WIRES, AN EXHAUST TUBE SEALED TO FORM A BLOW-HOLE AT THE SIDE OF THE BOTTOM OF SAID PRESS, A SUBSTANTIALLY FLAT GROOVE IN SAID PRESS AND EXTENDING FROM SAID BLOW-HOLE TO THE TOP OF SAID PRESS, AND A LIP EXTENDING OUTWARDLY OVER SAID GROOVES FROM THE TOP OF SAID PRESS. 